Windows with tilt sash supported by counterbalanced shoes have used a variety of shoe locks for holding the shoes in place within jamb liner channels when a sash is tilted, and many of these locking systems have used biters that bite into the plastic surfaces of jamb liners that are formed of extruded resin material. Although there are many previous suggestions for such biting lock shoe systems, including U.S. Pat. Nos. 3,197,819; 3,233,278; 3,524,282; 3,797,168; 4,271,631; 4,799,333; and 4,885,871, all of these have suffered from one or more of the following problems: lack of reliability in holding the shoes in place against counterbalance spring force when a sash is tilted or removed; inability to accommodate all the mishaps associated with window installation, including bowed jambs and dry wall dust or other debris entering the shoe channels; parts failures requiring expensive repairs or replacements after windows are installed; lack of durability causing performance to diminish with use so that a sash no longer operates smoothly and locks correctly upon tilting; inconvenience in use requiring awkward manipulations of a sash or requiring that sash pins be replaced accurately into recesses in shoes locked in jamb liner channels; and expense or complexity resulting in an overly large manufacturing cost and selling price.
The tilt sash lock shoe system of this invention solves all these problems with a simple, inexpensive, and reliable biter shoe that is convenient to operate and readily endures the abuses encountered by windows. A preferred embodiment of this lock shoe system uses a single shoe that can accommodate sash tilt in either direction so that the one shoe can be installed on either side of a window.